* chore: change initial cover type's name to none
* chore: refactor cover node widget
* chore: use a constant instead of magic value
* fix: make the size of icon hover effect smaller
* chore: improve appearance of selected color
* test: add cover integration tests
* fix: inner ring of selected color in dark mode
* refactor: cover node to document header node
* test: simplify tests
* chore: rename files
